1. Field of the Invention
The present invention relates to a means of and method for controlling the tractive force in a motor-driven vehicle, such as a rail vehicle, comprising a drive wheel driven by a drive motor.
In a rail vehicle, the tractive force F varies with the difference .DELTA. v between the peripheral speed of the drive wheel and the speed of the vehicle. To a relatively great extent, the tractive force varies depending on the surface of the rails and drive wheels, or the existence of contaminations, rust, ice or the like and the speed of the vehicle. In principle, when the tractive force increases from zero up to a certain value F.sub.1 , the difference .DELTA. v between the peripheral speed of the drive wheel and the speed of the vehicle increases because of elastic deformations, relatively slowly up to a certain value .DELTA. v.sub.1 , which may be about 75 per cent of the maximum tractive force F.sub.max . If the tractive forces increases further, pronounced slipping occurs between the wheels and the rail. The maximum tractive force F.sub.max is obtained normally when the difference is 1 or a few km/hour, and decreases if the difference .DELTA. v increases further.
It is extremely desirable to be able to exploit the maximum available tractive force when necessary, that is, to be able to work in a stable manner with .DELTA. v = .DELTA. v.sub.2 , where of course F = F.sub.max . Since, as mentioned above, both .DELTA. v.sub.2 and F.sub.max , vary relatively widely with uncontrollable external conditions, it has so far been impossible to fulfil this desire. The invention provides a system by which this problem is solved in a simple and advantageous manner.
2. The Prior Art
It has been found that in the case of slipping various kinds of oscillations in the drive system - bogie unit occur. In the arrangement described in Nilsson application Ser. No. 407,508, filed Oct. 18, 1973, primarily one of these modes of oscillations is used, namely torsional oscillations in the system drive axle - drive wheel, which oscillations in a typical case have a natural frequency of around 50 Hz. For detecting these oscillations, the above-mentioned application describes the use of a force transducer, for example of a magnetoelastic or a strain gauge type, attached to a reaction stay, or accelerometers arranged on the bogie. As an alternative it is of course possible to use a torque transducer or a speed transducer (tachometer-generator), mounted on the drive axle or the drive wheels, for detecting these oscillations.